Field of the Invention
The present invention relates to an RF resource allocation technique, and particularly relates to an RF resource allocation technique by which an RF resource allocation device notifies a mobile terminal of an RF resource to be used.
Description of the Related Art
In recent years, a mobile terminal (movable radio communication device) is equipped for a plurality of radio frequencies and radio communication methods, and increases the efficiency of communication and avoids congestion by performing the communication by using an appropriate communication parameter in accordance with conditions. A method for determining the communication parameter includes a distribution method in which the mobile terminal itself determines the communication parameter and a central control method in which a central server determines the communication parameter and notifies the mobile terminal of the determined communication parameter.
Each of Japanese Patent Application Laid-open No. 2009-200773 and U.S. Pat. No. 8,290,426 discloses a method for determining a frequency to be used by the distribution method. In this method, the mobile terminal detects an available frequency by scanning. At this point, the mobile terminal refers to a table in which the utilization probability of each frequency is indicated for each time and position, and an increase in efficiency is achieved by scanning the frequencies in descending order of the utilization probability.
One of the problems of the distribution method is that the mobile terminal cannot recognize global communication conditions. There are cases where a lack of a global viewpoint leads to the hidden node problem. In addition, when a plurality of the mobile terminals perform the scanning independently of each other, there are cases where the mobile terminals simultaneously start transmission by using the same channel, which leads to the loss of messages of both terminals. As the utilization rate of the channel is higher, the problem gets more severe.
The central control method is used in a mobile phone network and the like. A system that uses a white space database (WSDB) (Google Inc. “Proposal by Google Inc. to Provide a TV Band Device Database Management Solution”, [online], [retrieved on Mar. 3, 2016], <URL: http://www.scribd.com/doc/24784912/01-04-10-Google-White-Spaces-Database-Proposal>) is one of the central control methods. In the mobile phone network, the mobile terminal and a base station need to cooperate with each other closely and communicate with each other bidirectionally. In the case of WSDB, white space information is distributed by broadcast, and it is not necessary to transmit data from the mobile terminal to WSDB. However, in the system that uses WSDB, static white space information based on the position of a broadcast station is sent, and it is difficult to control the communication parameter in accordance with the real-time communication conditions.
Patent Document 1: Japanese Patent Application Laid-open No. 2009-200773
Patent Document 2: U.S. Pat. No. 8,290,426
Patent Document 3: U.S. Pat. No. 7,983,841
Patent Document 4: U.S. Pat. No. 8,483,700
Patent Document 5: U.S. Pat. No. 8,874,123
Patent Document 6: U.S. Pat. No. 6,965,576
Non-Patent Document 1: Google Inc. “Proposal by Google Inc. to Provide a TV Band Device Database Management Solution”, [online], [retrieved on Mar. 3, 2016], <URL: http://www.soribd.com/doc/24784912/01-04-10-Google-White-Space s-Database-Proposal>